Variable mode jet engine - compact

ABSTRACT

This Jet engine comprises of a complete low bypass turbofan unit  1  including secondary fan unit  2  and engine core, some five to eight feet ahead of which sits a larger diameter main fan unit  3  driven from the secondary fan via drive shaft  4 . Between the main and secondary fans sits a reversed variable area nozzle  5  connected to the forward end of the secondary fan by a short inlet tube  6  (fitted with intercooler  12 ). At the back of the core sits another variable area nozzle  7  facing rearwards. This arrangement (front nozzle, inlet tube, secondary fan, core, rear nozzle) is enclosed by a variable diameter cylinder  8 , providing a variable area bypass duct  9  between cylinder and engine outer casing  10  that extends backwards from the outer diameter of the main fan. A third variable area nozzle  11  is positioned aft of the outer casing facing rearwards.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0002] Not Applicable

REFERENCE TO MICROFICHE APPENDIX

[0003] Not Applicable

BACKGROUND OF THE INVENTION

[0004] This invention relates to a variable mode (turbofan, turbojet, ramjet) type jet engine, which is suitable for compact installation. Jet engines are normally built in fixed mode either as turbofans, turbojets or ramjets, this invention sets out to combine all types of engine.

BRIEF SUMMARY OF THE INVENTION

[0005] According to the present invention there is provided a jet engine comprising of a complete low bypass turbofan unit including (secondary) fan unit and engine core (compressors, combustion chamber, turbines and secondary bypass duct), some five to eight feet ahead of which sits a larger diameter (main) fan unit driven from the front of the secondary fan via a short drive shaft. Between the main fan and the secondary fan sits a reversed (front inner) variable area nozzle connected to the forward end of the secondary fan in line by a short inlet tube, and arranged to form a ram from the main fan into the secondary fan when open. At the back of the engine core sits another (rear inner) variable area nozzle facing rearwards in line. The whole of this arrangement (front inner nozzle, inlet tube, secondary fan, engine core, secondary bypass duct and rear inner nozzle) is enclosed by a variable diameter cylinder, providing for the main variable area bypass duct between the variable diameter cylinder and the engine outer casing, which extends backwards from the outer diameter of the main fan and completely encloses the variable diameter cylinder within. A third (main) variable area nozzle is positioned aft of the outer casing facing rearwards. An intercooler would be fitted in line in or around the inlet tube just ahead of the secondary fan to cool down the incoming air charge.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0006]FIG. 1 illustrates the low bypass turbofan/ramjet mode (ramfan); the front and rear inner nozzles and variable diameter cylinder would be completely expanded, with the main bypass area totally closed off, thereby ramming the airflow from the main fan into the secondary fan and hence supercharging the secondary fan and engine core at subsonic speeds, and forming a ramjet at supersonic speeds, albeit with rotating inner parts. There would be no need for an afterburner on this type of engine.

[0007]FIG. 2 illustrates the transition between modes and intermediate bypass mode; at subsonic speeds the front and rear inner nozzles and variable diameter cylinder would be partially expanded, splitting the main fan thrust and thereby only partially supercharging and partially bypassing the secondary fan and engine core.

[0008]FIG. 3 illustrates the high bypass turbofan mode; at subsonic speeds the front and rear inner nozzles and variable diameter cylinder would be totally contracted allowing the outer portion of the main fan to completely bypass the secondary fan and engine core.

DETAILED DESCRIPTION OF THE INVENTION

[0009] Referring to the drawing there is provided a jet engine comprising of a complete low bypass turbofan unit 1, including (secondary) fan unit 2 and engine core (compressors, combustion chamber, turbines and secondary bypass duct 14), some five to eight feet ahead of which sits a larger diameter (main) fan unit 3 driven from the front of the secondary fan via a short drive shaft 4. Between the main fan and the secondary fan sits a reversed (front inner) variable area nozzle 5 connected to the forward end of the secondary fan in line by a short inlet tube 6, and arranged so that the variable end faces forwards and is positioned just behind the main fan and forms a ram into the secondary fan. See FIG. 2.

[0010] At the back of the engine core sits another (rear inner) variable area nozzle 7 facing rearwards in line. The whole of this arrangement (front inner nozzle, inlet tube, secondary fan, engine core, secondary bypass duct and rear inner nozzle) is enclosed by a variable diameter cylinder 8, providing for the main variable area bypass duct 9 between the cylinder and the engine outer casing 10, which extends backwards from the outer diameter of the main fan and completely encloses the variable diameter cylinder within. A third (main) variable area nozzle 11 is positioned aft of the outer casing facing rearwards. See FIG. 2

[0011] An intercooler 12 would be fitted in line in or around the short inlet tube ahead of the secondary fan to cool down the incoming air charge. The engine core would have a two-stage combustion chamber 13 so as to ignite the extra oxygen provided by the main fan supercharging effect in low bypass turbofan mode. See FIG. 1 and 2.

[0012] The ideal main bypass ratio for this type of engine would be around 1.6:1. The ideal secondary bypass ratio for this type of engine would be zero, but this would not allow for cooling of the engine core and rear exhaust.

[0013] The large main fan in this design has in effect replaced the afterburner normally provided for on a conventional low bypass turbofan.

[0014] It would not be possible to replace a normal afterburning low bypass type jet engine directly with this type of engine in the same airframe. For example, replacing an engine, equally, with an inlet diameter of 34 inches would only produce a static thrust of about 21000 pounds (supercharged low bypass turbofan mode) for this type of engine. In this instance the main fan diameter would need to be increased to about 39 inches, so as to produce around 28500 pounds of static thrust. Below are some typical figures for this type of engine: Main fan diameter 46 inches Secondary fan diameter 28 inches Main bypass ratio 1.35:1 Secondary bypass ratio 0.20:1 Static power from main fan (High bypass turbofan mode) 13500 pounds Static power from rear turbofan (High bypass turbofan mode) 13500 pounds Static combined power (High bypass turbofan mode) 27000 pounds Static combined power (Supercharged low bypass turbofan mode) 40500 pounds 

1. What I claim as my invention is a jet engine comprising of a complete low bypass turbofan unit including (secondary) fan unit and engine core (compressors, combustion chambers, turbines and secondary bypass duct), some five to eight feet ahead of which sits a larger diameter (main) fan unit driven from the front of the secondary fan via a short drive shaft, between the main fan and the secondary fan sits a reversed (front inner) variable area nozzle connected to the forward end of the secondary fan by a short in line inlet tube, at the back of the engine core sits another (rear inner) variable area nozzle facing rearwards in line, the whole of this arrangement (front inner nozzle, inlet tube, secondary fan, core, secondary bypass duct and rear inner nozzle) is enclosed by a variable diameter cylinder providing for the main variable area bypass duct between the variable diameter cylinder and the engine outer casing which extends backwards from the outer diameter of the main fan and completely encloses the variable diameter cylinder within, a third (main) variable area nozzle is positioned aft of the outer casing facing rearwards, an intercooler would be fitted in or around the inlet tube just ahead of the secondary fan.
 2. A jet engine as claimed in claim 1 wherein there is provided for a main fan or fans placed a short distance ahead of a smaller diameter secondary fan or fans and engine core, the main fan or fans would be driven from the front of the secondary fan or fans via a short drive shaft or shafts.
 3. A jet engine as claimed in claim 2 wherein there is provided for a short inlet tube of the same diameter as the secondary fan or fans placed ahead of the secondary fan or fans and a short distance behind the main fan or fans, attached to the forward part of this tube would be a reversed variable area (front inner) nozzle fitted to the short inlet tube by its fixed end with the variable forward end situated just behind the main fan or fans and arranged so as to be of the same diameter as the main fan when fully opened and to form a ram into the secondary fan or fans and engine core.
 4. A jet engine as claimed in claim 3 wherein there is provided for an intercooling device fitted in or around the short inlet tube and between the front inner nozzle and the secondary fan or fans, to cool down the incoming air charge.
 5. A jet engine as claimed in claim 4 wherein there is provided for a secondary bypass duct fitted behind the secondary fan or fans and around the engine core.
 6. A jet engine as claimed in claim 5 wherein there is provided for a two-stage combustion chamber within the engine core.
 7. A jet engine as claimed in claim 6 wherein there is provided for a second variable area (rear inner) nozzle fitted to the rear of the secondary bypass duct by its fixed end, with the variable end pointing towards the rear and arranged so as to be of a larger diameter than the secondary bypass duct when fully opened.
 8. A jet engine as claimed in claim 7 wherein there is provided for an arrangement whereby the front inner nozzle, inlet tube, secondary fan or fans, engine core, secondary bypass duct and rear inner nozzle are all completely enclosed by a variable diameter cylinder, fitted at the front end to the forward part of the front inner nozzle and fitted at the back to the rearwards end of the rear inner nozzle.
 9. A jet engine as claimed in claim 8 wherein there is provided for a main engine casing extending backwards from the rear of the main fan or fans and enclosing the whole of the variable diameter cylinder and hence forming the main variable bypass duct between this casing and the enclosed variable diameter cylinder, this main engine casing is intended to be an integral part of the airframe.
 10. A jet engine as claimed in claim 9 wherein there is provided for a third (main) variable area nozzle fitted to the rear of the main engine casing by its fixed end with the variable end pointing rearwards and arranged so as to be of a smaller diameter than the main engine casing when closed.
 11. A jet engine substantially as described herein with reference to FIGS. 1, 2 and 3 of the accompanying drawings. 